Kathy Kaelin, age 11s, of Philadelphia her question:
What is a white dwarf?
No, this is not a character from a fairy story. It is a star a test amazing star. Suppose we could reach a white dwarf star and grab a container of the gases from which it is made. A pint bottle of this material would weigh about twenty tons. A thimbleful would weigh about half a ton. A white dwarf is made of material which may be 60,000 times as heavy as water or 6,000 times denser than platinum.
It is no surprise to learn that some stars are bigger and brighter than others for that is how they look in the sky. But it may be a surprise to learn that stars are not classed from the way they look from the earth. A small neighbor star may look brighter than a faraway bigger star. Astronomers must first know the distance of a star before it can be classed according to its sizes its temperature and maybe the gaseous elements it contains, Most of the work of classifying the stars has been done in the present century.
The great majority of stars, like our sun, fall into the average class. But there are giants, supergiants and there are dwarfs. It seems, however, that the stars do not vary a great deal in mass the bulky matter they contain. The red giant star Betelguese is 540 times the diameter of our sun and big enough to swamp almost half of our Solar System. Yet its mass is only 15 times greater than that of our sun.
The gassy material in such a star, then, is very thin almost like a near vacuum. The most famous of the white dwarf stars is the companion of Sirius the Dog Star. It is called Sirius B, alias the Pup. The diameter of the Pup is estimated to be about 25,000 miles which makes it quite a bit smaller than Neptune, the fourth largest planet of our Solar System.
In fact, when it comes to size, the Pup is less than four times the size of the planet earth.
But what a difference when it comes to weight. The mass of the little Pup is four fifths the mass of the sun. On a pair of celestial scales, the little star would weigh 96 per cent as much as the sun. Yet the sun is about 1,300,000 times bigger than the earth and the Pup is less than four times bigger than the earth.
Obviously the material in the Pup must be packed very tight indeed. It is some 27,000 times more dense than the material in the sun. The very atoms themselves must be especially packed. A normal atom is a nucleus with a number of widely separated electrons there is plenty of space between the particles. In the gases of a white dwarf, the space may be eliminated. Perhaps the atomic nuclei are stripped of their electrons and packed close together.
At first it was thought that the Pup was a cool. star, for it gives off little light. Later it was learned that this is because it cannot radiate much brilliance from its small surface. Far from being cool, a white dwarf is very, very hot not red hot but white hot.